This doesn't look like the world's most convincing leak. And not just because Qualcomm said 8-core SoCs were dumb. If true this would be the first SoC with 8 legitimate higher end mobile cores. They don't even get an added flexibility benefit since they already have separate DVFS for each core. Which would add a lot of complexity
They also don't have the power budget to run 8 cores at anywhere remotely near 2.5GHz in something like a BlackBerry phone, even on 20nm, which will only have modest efficiency improvements over 28nm anyway. They'd get a bit of a boost in worthless benchmarks like AnTuTu but not a huge one, and that'd be about it. Not worth the huge premium in die area and complexity for both the SoC and PMIC. The process shrink does give them some more transistors to play with for similar package sizes, but they'd be better off spending it on enhancements that improve core perf/MHz and GPU performance.
I think when anyone goes for > 4 higher end, homogeneous cores in an SoC it'd make sense to hit 6 cores first.